Paladin: Being able to snack on undead for a healing boost completely changes the way you approach the map. The guaranteed HalpMeh glyph effectively turns off poison and lets you start challenging higher-level monsters from the very start

Rogue: The high damage, low health attributes of the Rogue make it feel like you're playing another game altogether

Thief: A cool 'everyman' class that has lots of utility powers but almost no combat powers (stabber is so weak that it barely counts), but still somehow comes out as one of the best classes in the game.

I voted for rogue (orc) just because with some simple preps and a god like Taurog, they get ridiculously powerful early on, and I tend to win more often with a Rogue. Give them Cydestep and they are practically invincible.